Low vs High current sensing

Discussion in 'General Electronics Chat' started by Mad I.D., May 20, 2010.

  1. Mad I.D.

    Thread Starter New Member

    Apr 15, 2010
    Hi guys,
    I'm implementing a current sensing and have a doubt whether I should use high or low side method. I'm building a programmable power supply module which will deliver power via standard coaxial cables with SMA connectors. One more cable will be used to measure the DUT's voltage differentially. (kind of a sense input)

    I have read a lot of material concerning this, but two things still puzzles me:

    1) "They say" that low side sense resistors created ground EMI which is not tolerable. What is the difference between the noise on the ground path and the same noise at the positive rail? My resistor would be 100mR, but there is already 20-30mR of outer conductor resistance here so I just making thinks a little worse.

    2) Unsafe since it cannot detect accidental short which would bypass the sense resistors. I think this can never happed in my case, but still it puzzles me, am I right?

    Thanks guys.
  2. retched

    AAC Fanatic!

    Dec 5, 2009
    If you are talking about non-contact current sensing, It wont work with coax. The 2 conductors will cancel each other out. You have to run a single wire through the loop or clamp.

    I just noticed you were talking about the current sensing resistors, I would avoid them in the case that EMI ends up being intolerable. Or use resistors with the lowest amount of EMI. Wire wound is out, as they are basically EMI generators.

    I dont know how accurate a toroidal / on board non contact current sensor would do. A ferrite bead and, depending on the placement on the board, I would put it as close to the ground connection to the power supply (gnd) connector.
    Last edited: May 22, 2010